Techniques (pattern-forming techniques) in which a fine pattern is formed on top of a substrate, and a lower layer beneath that pattern is then fabricated by conducting etching with this pattern as a mask are widely used in the semiconductor industry for IC fabrication and the like, and are attracting considerable attention. These types of fine patterns are usually formed from an organic material, and are formed, for example, using a lithography method or a nanoimprint method or the like. For example, in the case of a lithography method, a resist film composed of a resist material that exhibits a changed solubility in a developing solution upon exposure is formed on top of a supporting material such as a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. Using this resist pattern as a mask, a semiconductor or the like is produced by conducting a step in which the substrate is processed by etching.
A resist material in which the exposed portions exhibit increased solubility in a developing solution is called a positive-type, and a resist material in which the exposed portions exhibit decreased solubility in a developing solution is called a negative-type.
In recent years, advances in lithography techniques have led to rapid progress in the field of pattern miniaturization. Typically, these miniaturization techniques involve increasing the energy (for example, shortening the wavelength) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having higher energy than these excimer lasers, such as electron beam, extreme ultraviolet radiation (EUV), and X ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources. As a resist material which satisfies these conditions, a chemically amplified resist composition containing an acid generator that generates acid upon exposure is used. In addition to the acid generator, the chemically amplified resist composition generally includes a base component that exhibits changed solubility in an alkali developing solution by the action of acid generated from the acid generator. For example, as a base component for the positive chemically amplified resists, a base component that exhibits increased solubility in an alkali developing solution under the action of acid has been used (see, for example, Patent Document 1). Resins are mainly used as a base component for the chemically amplified resist compositions.
As a technique for further improving the resolution of resist patterns, a lithography method called liquid immersion lithography (hereafter, frequently referred to as “immersion exposure”) is known in which exposure (immersion exposure) is conducted in a state where the region between the objective lens of the exposure apparatus and the sample is filled with a solvent (an immersion medium) that has a larger refractive index than the refractive index of air (see, for example, Non-Patent Document 1).
According to this type of immersion exposure, it is considered that higher resolutions equivalent to those obtained using a shorter wavelength light source or a larger NA lens can be obtained using the same exposure light source wavelength, with no lowering of the depth of focus. Furthermore, immersion exposure can be conducted using a conventional exposure apparatus. As a result, it is expected that immersion exposure will enable the formation of resist patterns of higher resolution and superior depth of focus at lower costs. Accordingly, in the production of semiconductor devices, which requires enormous capital investment, immersion exposure is attracting considerable attention as a method that offers significant potential to the semiconductor industry, both in terms of cost and in terms of lithography properties such as resolution.
Immersion lithography is effective in forming patterns having various shapes. Further, immersion exposure is expected to be capable of being used in combination with currently studied super-resolution techniques, such as phase shift method and modified illumination method. Currently, as the immersion exposure technique, technique using an ArF excimer laser as an exposure source is being actively studied. Further, water is mainly studied as the immersion medium.
As a lithography technique which has been recently proposed, a double patterning method is known in which patterning is conducted two or more times to form a resist pattern (for example, see Non-Patent Documents 2 and 3). According to the double patterning process, for example, a first resist film is formed on a substrate, and patterning of the first resist film is conducted to form a plurality of resist patterns. Then, a second resist material is applied to the plurality of resist patterns to form a second resist film which fills the gaps between the plurality of resist patterns. Then, by conducting patterning of the second resist film, it is presumed that a resist pattern can be formed with a higher resolution than the resist pattern formed by the first patterning.